Aqueous solutions of carbohydrate origin are encountered widely in industry in which naturally-occurring carbohydrate-containing materials are processed to give useful products. Examples of such processes include industrial reactions in which carbohydrates are broken down enzymatically or analogous processes in which the breakdown takes place by chemical action. The products of such processes are often obtained in the form of aqueous solutions comprising suspended by-product material which is separated by filtration. Problems are frequently encountered in such filtrations and it is often difficult to obtain a filtrate free from cloudiness. We have now found that the problems are often caused by the presence in the aqueous solutions of certain phosphorus-containing compounds and the present invention comprises a process for dealing with such compounds so that the filterability of the aqueous solutions is improved.
We have found in particular that the process of the invention is applicable to solutions in which the carbohydrate is starch which has been subjected to a hydrolytic process. For reasons of convenience, the process of the invention will be described subsequently in this specification in terms of starch although it should be borne in mind that the process and process conditions are applicable to aqueous solutions derived from other carbohydrates.
Starch is a high polymer carbohydrate made up of glucopyranose units joined together by alpha-glucosidic linkages. The polymer may be broken down by hydrolysis to yield lower molecular weight oligosaccharides and ultimately the monomer unit, glucose. The hydrolysis may be catalysed by acids or by enzymes, acids and alpha-amylases causing a more or less random cleavage of the starch molecule by hydrolysing the alpha-D-(1-&gt;4) glucosidic bonds. Beta-amylases are more specific in their action, splitting-off maltose directly from the starch or oligosaccharide molecule while glucoamylases are capable of splitting-off D-glucose (dextrose). Debranching enzymes, e.g., pullulanase, may also be used to facilitate the hydrolysis of the amylopectin starch component.
The so-called starch syrups are starch hydrolysates which are produced from starch by acid and/or enzymatic hydrolysis and which generally contain dextrose and/or maltose with trimers and other oligomers up to DP 20 or even higher ("DP" is "degree of polymerisation" and is followed by a digit(s) indicating the number of monomer units in the molecule). The hydrolysates have a range of compositions and a variety of uses many of which require the syrup to be clear and almost colorless.
We have encountered problems in the production of such syrups, particularly from wheat starch, finding that the hydrolysis product is very difficult to filter using standard equipment and that the filtrate is unacceptably cloudy. We have found, following an extensive investigation, that the problem is caused by the presence of phospholipids and that the filtration rate and clarity of a starch hydrolysate may be improved by treatment with certain enzymes.